Low current RRAM-based crossbar array circuits implemented with interface engineering technologies

ABSTRACT

Interface engineering technologies relating to low current RRAM-based crossbar array circuits are disclosed. An apparatus, in some implementations, includes: a substrate; a bottom electrode formed on the substrate; a first geometric confining layer formed on the bottom electrode. The first geometric confining layer comprises a first plurality of pin-holes. The apparatus further comprises a base oxide layer formed on the first geometric confining layer and connected to a first top surface of the bottom electrode via the first pin-holes; and a top electrode formed on the base oxide layer. The base oxide layer comprises one of: TaO x , HfO x , TiO x , ZrO x , or a combination thereof; the first geometric confining layer comprises Al 2 O 3 , SiO 2 , Si 3 N 4 , Y 2 O 3 , Gd 2 O 3 , Sm 2 O 3 , CeO 2 , Er 2 O 3 , or a combination thereof.

TECHNICAL FIELD

The present disclosure relates generally to crossbar array circuits withone or more Resistive Random-Access Memories (RRAMs) and morespecifically to low current RRAM-based crossbar array circuitsimplemented with switching oxide engineering technologies.

BACKGROUND

Conventionally, a crossbar array circuit may include horizontalelectrode rows and vertical electrode columns (or other electrodes)intersecting with each other, with crossbar devices formed at theintersecting points. The crossbar array may be used in non-volatilesolid-state memory, signal processing, control systems, high-speed imageprocessing, neural network, and other applications.

An RRAM is a two-terminal passive device that is capable of changing itsresistance responsive sufficient electrical stimulations. Thesecharacteristics have attracted significant attention forhigh-performance nonvolatile memory applications. The resistance of theRRAM may be electrically switched between two states: a High-ResistanceState (HRS) and a Low-Resistance State (LRS). Switching an RRAM from anHRS to an LRS may be referred to as a “Set” or “On” operation.Conversely, switching an RRAM from an LRS to an HRS may be referred toas a “Reset” or “Off” operation.

RRAMs implemented in crossbar arrays may provide In-Memory Computing(IMC) capabilities due to their multilevel capability and stability ofeach resistance level. To provide IMC architectures using RRAM-basedcrossbar array circuit, such capabilities as providing analog behaviors,a multi-states storage, ultra-low power consumption, and progressivevoltage/current programming are desired.

Further, in filamentary RRAMs, after a filament is formed within anRRAM, the resistance of RRAM in LRS becomes and remains low, resultingin high currents within the RRAM, rendering the RRAM undesirable for lowenergy applications.

Providing desirable technical features in low current RRAM-basedcrossbar array circuits thus remain technically challenging.

SUMMARY

Interface engineering technologies relating to low current RRAM-basedcrossbar array circuits are disclosed.

An apparatus, in some implementations, includes: a substrate; a bottomelectrode formed on the substrate; a first geometric confining layerformed on the bottom electrode. The first geometric confining layercomprises a first plurality of pin-holes. The apparatus furthercomprises a base oxide layer formed on the first geometric confininglayer and connected to a first top surface of the bottom electrode viathe first pin-holes; and a top electrode formed on the base oxide layer.The base oxide layer comprises one of: TaO_(x), HfO_(x), TiO_(x),ZrO_(x), or a combination thereof; the first geometric confining layercomprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂, Er₂O₃, or acombination thereof.

The apparatus, in some implementations, includes: the base oxide layeris at least three times as thick as the first geometric confining layer.

The apparatus, in some implementations, further includes a secondgeometric confining layer formed on the base oxide layer. The secondgeometric confining layer comprises a second plurality of pin-holes, andthe top electrode is formed on the second geometric confining layer andis connected to a second top surface of the base oxide layer via thesecond pin-holes.

In some implementations, the base oxide layer is at least three times asthick as the second geometric confining layer.

In some implementations, the second geometric confining layer comprisesAl₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂, Er₂O₃, or a combinationthereof.

In some implementations, the second geometric confining layer and thefirst geometric confining layer are made of different materials.

In some implementations, the substrate comprises Si, Si₃N₄, SiO₂, Al₂O₃,or a combination thereof.

The apparatus, in some implementations, further includes: a column wireconnected to the bottom electrode; and a row wire connected to the topelectrode.

An apparatus, in some implementations, includes: a substrate; a bottomelectrode formed on the substrate; a base oxide layer formed on thebottom electrode; a first geometric confining layer formed on the baseoxide layer. The first geometric confining layer comprises a firstplurality of pin-holes. The apparatus further includes a top electrodeformed on the first geometric confining layer and contacted to a firsttop surface of the base oxide layer via the first plurality ofpin-holes. The base oxide layer comprises TaO_(x), HfO_(x), TiO_(x),ZrO_(x), or a combination thereof; the first geometric confining layercomprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂₀₃, CeO₂, Er₂O₃, or acombination thereof.

In some implementations, the base oxide layer is at least three times asthick as the first geometric confining layer.

An apparatus, in some implementations, includes: a substrate; a bottomelectrode formed on the substrate; a first base oxide layer formed onthe bottom electrode; a first geometric confining layer formed on thefirst base oxide layer. The first geometric confining layer comprises afirst plurality of pin-holes. The apparatus further includes a secondbase oxide layer formed on the first geometric confining layer andconnected to a first top surface of the first base oxide layer via thefirst plurality of pin-holes; and a top electrode formed on the secondbase oxide layer. The first base oxide layer comprises TaO_(x), HfO_(x),TiO_(x), ZrO_(x), or a combination thereof; the first geometricconfining layer comprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂,Er₂O₃, or a combination thereof.

In some implementations, the first base oxide layer is at least threetimes as thick as the first geometric confining layer.

In some implementations, the second base oxide layer is at least threetimes as thick as the first geometric confining layer.

In some implementations, the second base oxide layer comprises TaO_(x),HfO_(x), TiO_(x), ZrO_(x), or a combination thereof.

In some implementations, the second base oxide layer and that of thefirst base oxide layer are made of different materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an example crossbar arraycircuit in accordance with some implementations of the presentdisclosure.

FIG. 1B is a block diagram illustrating a partially enlarged view of theexample crossbar device shown in FIG. 1A in accordance with someimplementations of the present disclosure.

FIG. 2 is a block diagram illustrating an example RRAM cell inaccordance with some implementations of the present disclosure.

FIG. 3 is a block diagram illustrating a second example RRAM cell inaccordance with some implementations of the present disclosure.

FIG. 4 is a block diagram illustrating a third example RRAM cell inaccordance with some implementations of the present disclosure.

FIG. 5 is a block diagram illustrating a fourth example RRAM cell inaccordance with some implementations of the present disclosure.

The implementations disclosed herein are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings. Like reference numerals refer to corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Technologies relating to low current RRAM-based crossbar array circuitswith interface engineering are disclosed. The technologies described inthe present disclosure may provide the following technical advantages.

First, the disclosed technologies increase the resistance of a lowcurrent RRAM in both the LRS and the HRS. This resistance increase maydecrease the Set/Reset current and the reading currents of theresistance levels with a certain reading voltage, which increases theoverall power efficiency, a desirable feature for IMC applications.

Second, the disclosed technologies do not require modifications beyondthe interface between a base oxide and an electrode, reducing thecomplexity for manufacturing such RRAMs and thus increasing theproduction reliability and the production yield.

FIG. 1A is a block diagram 1000 illustrating an example crossbar arraycircuit 110 in accordance with some implementations of the presentdisclosure. As shown in FIG. 1A, the crossbar array circuit 110 includesa first row wire 101, a first column wire 102, and a crossbar device103.

FIG. 1B is a block diagram 1500 illustrating a partially enlarged viewof the crossbar device 103 in accordance with some implementations ofthe present disclosure. In FIG. 1B, the crossbar device 103 is connectedto the first row wire 101 and to the first column wire 102. In someimplementations, the crossbar device 103 includes an RRAM cell 1031. TheRRAM cell 1031 may be connected to a transistor to form aone-Transistor-one-memristor (1T1R) stack, or to a selector to form aone-Selector-one-memristor (1S1R) stack, or a single memristor (1R)stack.

FIG. 2 is a block diagram 2000 illustrating an example RRAM cell 200 inaccordance with some implementations of the present disclosure.

As shown in FIG. 2 , the RRAM cell 200 includes a substrate 201, abottom electrode 203 formed on the substrate 201, a switching oxidestack 205 formed on the bottom electrode 203, and a top electrode 207formed on the switching oxide stack 205.

The switching oxide stack 205 includes a geometric confining layer 2053formed on the bottom electrode 203, and a base oxide layer 2051 formedon the geometric confining layer 2053 and the bottom electrode 203. Thegeometric confining layer 2053 may be a non-continuous layer thatincludes a predefined number of pin-holes 20531. The base oxide layer2051 may be filled and formed in the pin-holes 20531 and connected to atop surface 2031 of the bottom electrode 203. The conductive filamentformed within the RRAM cell 200 may be configured to grow and form onregions in alignment with these pin-holes 20531. In these ways, thecontact resistance of the RRAM cell 200 may be increased, because thecontact area is narrowed. These confined interfaces may produce a lowercurrent RRAM.

In some implementations, the substrate 201 is made of at least one ofthe following materials: Si, Si₃N₄, SiO₂, Al₂O₃, or a combinationthereof. In some implementations, the bottom electrode 203 is made of:Ag, Al, Au, Cu, Fe, Ni, Mo, Pt, Pd, Ti, TiN, TaN, W, Zr, Ir, Ru, acombination thereof, or an alloy of any of these materials with anyother electrically conductive materials. In some implementations, thetop electrode 207 is made of: Ag, Al, Au, Cu, Fe, Ni, Mo, Pt, Pd, Ti,TiN, TaN, W, Zr, Ir, Ru, a combination thereof, or an alloy of any ofthese materials with any other electrically conductive materials.

In some implementations, the switching oxide stack 205 functions as afilament forming stack, within which one or more filaments may form. Thetop electrode 207 may be made of a reactive material: Ta, Hf, Zr, Ti,Ru, a combination thereof, or an alloy of any of Ta, Hf, Zr, Ti, Ru withany other electrically conductive materials; the bottom electrode 203may be made of a non-reactive material: Pt, Pd, Ir, TiN, TaN, acombination thereof, or an alloy of any of Pt, Pd, Ir, TiN, TaN with anyother electrically conductive materials. Under appropriate thermodynamicand kinetic conditions, metal from a reactive electrode may form oxygenvacancies in the switching oxide stack 205 and form a switching filamentwithin the switching oxide stack 205.

In some implementations, a reactive material has a higher oxygensolubility and mobility than those of a switching oxide and a filament.A reactive material may create oxygen vacancies in a switching oxide andform a filament solid solution containing oxygen. A reactive materialmay include one of: Ta, Hf, Ti, Zr, Ru, a combination thereof, or analloy of any of Ta, Hf, Ti, Ru and Zr with any other electricallyconductive materials.

In some implementations, a non-reactive has a higher chemical stabilitythan those of a switching oxide and a filament. A non-reactive materialmay include noble metal material such as: Pt, Pd, Ir, a combinationthereof, or an alloy of any of Pt, Pd, Ir, with any other electricallyconductive materials. A non-reactive material may also include metalnitride material such as: TiN, TaN, a combination thereof, or an alloyof any of TiN and TaN with any other electrically conductive materials.

As shown in FIGS. 1A-1B, in some implementations, a bottom electrode maybe a column wire or may be connected to a column wire; a top electrodemay be a row wire or may be connected to the row wire.

As shown in FIG. 2 , in some implementations, the switching oxide stack205 may be made of TaOx, HfOx, TiOx, ZrOx, or a combination thereof. Theswitching oxide stack 205, in some implementations, is a filamentforming stack. For example, when a Set signal (e.g. a Set voltage) isapplied, a conductive filament may form within the switching oxide stack205.

In some implementations, the base oxide layer 2051 may be made ofTaO_(x), HfO_(x), TiO_(x), ZrO_(x), or a combination thereof. In someimplementations, the geometric confining layer 2053 may be made ofAl₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂, Er₂O₃, or a combinationthereof. In some implementations, the geometric confining layer 2053 ismade of materials that are more stable than that of the base oxide layer2051.

The geometric confining layer 2053 may be formed between the base oxideand the bottom electrode to confine the area a conductive filamentcontacting the bottom electrode. The geometric confining layer 2053 mayreduce the effective filament size or reduce the size of the contactarea between a filament and an electrode, thereby reducing the operatingcurrent and increasing the contact resistance. The geometric confininglayer 2053 may have a thickness that is insufficient to form acontinuous layer. In some implementations, the geometric confining layer2053 includes one or more discrete islands (e.g., regions that aredisconnected from each other) or a film with a plurality of pin-holes.

The geometric confining layer 2053 may be made of a material that has arelatively large interfacial energy to the layer on which the geometricconfining layer 2053 grows. As a result, the geometric confining layer2053 does not grow uniformly on the surface or the interface between anelectrode and a base oxide. Rather, the geometric confining layer 2053may initially form one or more islands and then form a layer with aplurality of pin-holes, after the geometric confining layer 2053 growsthicker as a result of more materials being deposited.

In some implementations, the geometric confining layer 2053 is made ofAl₂O₃, and the base oxide layer 2051 is made of HfO_(x). Atomic LayerDeposition (ALD) technologies may be used to deposit the switching oxidestack 205. In some implementations, a few cycles of Al₂O₃ are depositedusing ALD technologies to form a geometric confining layer 2053, whichmay be approximately 0.2 to 0.7 nm thick. The 0.2 to 0.7 nm thick Al₂O₃film formed on certain materials with which high interfacial energiesare resulted the Al₂O₃ film may not be continuous. Next, HfO_(x) may bedeposited using ALD technologies to form a base oxide 2051 that isapproximately 3 nm thick. In some implementations, the thickness of thebase oxide layer 2051 is three times greater than that of the geometricconfining layer 2053. As such, the base oxide layer 2051 is thicker thanthe geometric confining layer 2053. This thickness difference allows aswitching oxide stack to maintain its filament forming mechanism.

FIG. 3 is a block diagram 3000 illustrating an RRAM cell 300 inaccordance with some implementations of the present disclosure.

As shown in FIG. 3 , the RRAM cell 300 includes a substrate 301, abottom electrode 303 formed on the substrate 301, a switching oxidestack 305 formed on the bottom electrode 303, and a top electrode 307formed on the switching oxide stack 305. The switching oxide stack 305,in some implementations, includes a base oxide layer 3051 formed on thebottom electrode 303 and a geometric confining layer 3053 formed on thebase oxide layer 3051.

The top electrode 307 is, in some implementations, formed on thegeometric confining layer 3053 and the base oxide layer 3051. Thegeometric confining layer 3053 may be a non-continuous layer thatincludes a plurality of pin-holes 30531. The top electrode 307, in someimplementations, is formed on the plurality of pin-holes 30531 and isconnected to a top surface 30511 of the base oxide layer 3051. Aconductive filament may form within the RRAM cell 300 and grow onregions in alignment with the pin-holes. Because the contact areabetween (1) the top electrode 307 and (2) the base oxide layer 3051 andthe bottom electrode 303 is reduced, the contact resistance isincreased. By implementing these interface engineering technologies, theRRAM cell 300 provides lower operating currents.

In some implementations, the geometric confining layer 3053 is made ofAl₂O₃, and the base oxide layer 3051 is made of HfO_(x). ALDtechnologies may be used to deposit the switching oxide stack 305. Insome implementations, HfOx may be deposited using ALD technologies toform the base oxide 3051, which may be less than approximately 3 nmthick. Next, a few cycles of Al₂O₃ may be deposited using ALDtechnologies to form the geometric confining layer 3053 for about 0.2 to0.7 nm. The Al₂O₃ film having a thickness around 0.2 to 0.7 nm may notbe continuous. In some implementations, the thickness of the base oxidelayer 3051 is three times greater than that of the geometric confininglayer 3053. As such, the base oxide layer 3051 may be thicker than thegeometric confining layer 3053. This thickness difference allows aswitching oxide stack to maintain its filament forming mechanism.

FIG. 4 shows a block diagram 4000 illustrating an RRAM cell 400 inaccordance with some implementations of the present disclosure.

As shown in FIG. 4 , the RRAM cell 400 includes a substrate 401, abottom electrode 403 formed on the substrate 401, a switching oxidestack 405 formed on the bottom electrode 403, and a top electrode 407formed on the switching oxide stack 405. The switching oxide stack 405includes a first base oxide layer 4051 formed on the bottom electrode403, a geometric confining layer 4053 formed on the first base oxidelayer 4051, and a second base oxide layer 4055 formed on the geometricconfining layer 4053 and the first base oxide layer 4051. The topelectrode 407 may be formed on the second base oxide layer 4055. Thegeometric confining layer 4053 may be a non-continuous layer thatincludes a plurality of pin-holes 40531. The second base oxide layer4055 may be filled and formed on the plurality of pin-holes 40531 andconnected to a top surface 40511 of the first base oxide layer 4051. Aconductive filament may form within the RRAM cell 400 and grow onregions in alignment with the plurality of pin-holes 40531. In theseways, the resistance of the RRAM cell 400 may be increased, because thecontact area between the first base oxide layer 4051 and the second baseoxide layer 4055 is reduced. These interface engineering technologiesenable a lower operating current for the RRAM cell 400.

In some implementations, the geometric confining layer 4053 is made ofAl₂O₃, and the first and second base oxide layers 4051 and 4055 are madeof HfO_(x). ALD technologies may be similarly used to deposit theswitching oxide stack 405. In some implementations, about 2 nm HfO_(x)may be deposited over bottom electrode 403 using ALD technologies toform the first base oxide 4051. Next a few cycles of Al₂O₃ may bedeposited using ALD technologies to form the geometric confining layer4053, which may be approximately 0.2 to 0.7 nm thick. The Al₂O₃ filmhaving a thickness of approximately 0.2 to 0.7 nm may not be continuous.Next, HfO_(x) may be deposited using ALD technologies to form the secondbase oxide layer 4055 for about 2 nm on the geometric confining layer4053 and the top surface 40511 of the first base oxide layer 4051.

In some implementations, the first base oxide layer 4051 is at leastthree times as thick as the geometric confining layer 4053; in someimplementations, the second base oxide layer 4055 is at least threetimes as thick as the geometric confining layer 4053. Thus, the firstbase oxide layer 4051 may be thicker than the geometric confining layer4053, and the second base oxide layer 4055 may also be thicker than thegeometric confining layer 4053. These interface engineering technologiesenable the switching oxide stack 405 to maintain its filament formingcapabilities, while providing an increased RRAM cell resistance.

Materials of which these layers may be the same or similar to theimplementations discussed with reference to FIGS. 2-3 . In someimplementations, the first base oxide layer 4051 and the second baseoxide layer 4055 may be made from different materials.

FIG. 5 shows a block diagram 5000 illustrating an RRAM cell 500 inaccordance with some implementations of the present disclosure.

As shown in FIG. 5 , the RRAM cell 500 includes a substrate 501, abottom electrode 503 formed on the substrate 501, a switching oxidestack 505 formed on the bottom electrode 503, and a top electrode 507formed on the switching oxide stack 505. The switching oxide stack 505includes a first geometric confining layer 5053 formed on the bottomelectrode 503, a base oxide layer 5051 formed on the first geometricconfining layer 5053 and a first top surface 5031 of the bottomelectrode 503, and a second geometric confining layer 5055 formed on thebase oxide layer 5051. The top electrode 507 is then formed on thesecond geometric confining layer 5055 and a second top surface 50511 ofthe base oxide layer 5051. The first geometric confining layer 5053 is anon-continuous layer that includes many first pin-holes 50531, and thesecond geometric confining layer 5055 is also a non-continuous layerthat includes many second pin-holes 50551. The base oxide layer 5051 isfilled and formed in the first pin-holes 50531 and contacted to thefirst top surface 5031 of the bottom electrode 503 via the firstpin-holes 50531. The top electrode 507 is filled and formed in thesecond pin-holes 50551 and contacted to a second top surface 50511 ofthe base oxide layer 5051 via the second pin-holes 50551. The conductivefilament formed within the RRAM cell 500 is configured to grow and formin regions in alignment with these pin-holes 50531 and 50551. In theseways, the contact resistance of the RRAM cell 400 may be increased,because the contact area between the bottom electrode 503 and the topelectrode 507 is narrowed. These interface engineering technologiesenable a lower operating current for the RRAM cell 400.

In some implementations, the first and second geometric confining layer5053 and 5055 are made of Al₂O₃, and the base oxide layer 5051 is madeof HfO_(x). ALD technologies may be similarly used to deposit theswitching oxide stack 505. In some implementations, 5 cycles of Al₂O₃may be deposited using ALD technologies to form the first geometricconfining layer 5053, which may be approximately 0.5 nm thick. The Al₂O₃film having a 0.5 nm thickness or less may not be continues, because anAl₂O₃ film becomes continuous when having a thickness greater than 1 nm.In some implementations, the base oxide layer 5051 is at least 3 timesas thick as the first geometric confining layer 5053, or the secondgeometric confining layer 5055, or both. As such, the base oxide layer5051 is thicker than the first geometric confining layer 5053, or thesecond geometric confining layer 5055, or both. This allows theswitching oxide stack 505 to maintain its filament forming capabilitieswith an increased resistance.

The materials used in the implementations described with reference toFIG. 5 may be the same or similar to the materials used in theimplementations described with reference to FIGS. 2-4 . The firstgeometric confining layer 5053 and the second geometric confining layer5055 may be made of different materials.

Plural instances may be provided for components, operations, orstructures described herein as a single instance. Finally, boundariesbetween various components, operations, and data stores are somewhatarbitrary, and particular operations are illustrated in the context ofspecific illustrative configurations. Other allocations of functionalityare envisioned and may fall within the scope of the implementation(s).In general, structures and functionality presented as separatecomponents in the example configurations may be implemented as acombined structure or component. Similarly, structures and functionalitypresented as a single component may be implemented as separatecomponents. These and other variations, modifications, additions, andimprovements fall within the scope of the implementation(s).

It will also be understood that, although the terms “first,” “second,”etc. may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used todistinguish one element from another. For example, a first column couldbe termed a second column, and, similarly, a second column could betermed the first column, without changing the meaning of thedescription, so long as all occurrences of the “first column” arerenamed consistently and all occurrences of the “second column” arerenamed consistently. The first column and the second are columns bothcolumn s, but they are not the same column.

The terminology used herein is for the purpose of describing particularimplementations only and is not intended to be limiting of the claims.As used in the description of the implementations and the appendedclaims, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “comprises” and/or “comprising,” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

As used herein, the term “if” may be construed to mean “when” or “upon”or “in response to determining” or “in accordance with a determination”or “in response to detecting,” that a stated condition precedent istrue, depending on the context. Similarly, the phrase “if it isdetermined (that a stated condition precedent is true)” or “if (a statedcondition precedent is true)” or “when (a stated condition precedent istrue)” may be construed to mean “upon determining” or “in response todetermining” or “in accordance with a determination” or “upon detecting”or “in response to detecting” that the stated condition precedent istrue, depending on the context.

The foregoing description included example systems, methods, techniques,instruction sequences, and computing machine program products thatembody illustrative implementations. For purposes of explanation,numerous specific details were set forth in order to provide anunderstanding of various implementations of the inventive subjectmatter. It will be evident, however, to those skilled in the art thatimplementations of the inventive subject matter may be practiced withoutthese specific details. In general, well-known instruction instances,protocols, structures, and techniques have not been shown in detail.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific implementations. However, theillustrative discussions above are not intended to be exhaustive or tolimit the implementations to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The implementations were chosen and described in order tobest explain the principles and their practical applications, to therebyenable others skilled in the art to best utilize the implementations andvarious implementations with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. An apparatus comprising: a substrate; a bottomelectrode formed on the substrate; a first geometric confining layerformed on the bottom electrode, wherein the first geometric confininglayer comprises a first film comprising a first plurality of pin-holes;a base oxide layer formed on the first geometric confining layer andconnected to a first top surface of the bottom electrode via the firstplurality of pin-holes; and a top electrode formed on the base oxidelayer, wherein the base oxide layer comprises one of: TaO_(x), HfO_(x),TiO_(x), ZrO_(x), or a combination thereof, wherein the first film ofthe first geometric confining layer comprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃,Gd₂O₃, Sm₂O₃, CeO₂, Er₂O₃, or a combination thereof, and wherein aconductive filament forms within the based oxide layer and in regions inalignment with the first plurality of pin-holes when a set signal isapplied to the top electrode and the bottom electrode.
 2. The apparatusas claimed in claim 1, wherein the base oxide layer is at least threetimes as thick as the first geometric confining layer.
 3. The apparatusas claimed in claim 1, further comprising: a second geometric confininglayer formed on the base oxide layer, wherein the second geometricconfining layer comprises a second film comprising a second plurality ofpin-holes, wherein the top electrode is formed on the second geometricconfining layer and is connected to a second top surface of the baseoxide layer via the second plurality of pin-holes, and wherein theconductive filament forms in the regions in alignment with the firstplurality of pin-holes and the second plurality of pin-holes.
 4. Theapparatus as claimed in claim 3, wherein the base oxide layer is atleast three times as thick as the second geometric confining layer. 5.The apparatus as claimed in claim 3, wherein the second geometricconfining layer comprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂,Er₂O₃, or a combination thereof.
 6. The apparatus as claimed in claim 5,wherein the second geometric confining layer and the first geometricconfining layer comprise different materials.
 7. The apparatus asclaimed in claim 5, wherein the second geometric confining layer and thefirst geometric confining layer comprise at least one common material.8. The apparatus as claimed in claim 1, wherein the substrate comprisesSi, Si₃N₄, SiO₂, Al₂O₃, or a combination thereof.
 9. The apparatus asclaimed in claim 1, further comprises: a column wire connected to thebottom electrode; and a row wire connected to the top electrode.
 10. Theapparatus as claimed in claim 1, wherein the first geometric confininglayer does not grow uniformly on a surface of the bottom electrode. 11.The apparatus as claimed in claim 10, wherein a thickness of the firstgeometric confining layer is between 0.2 nm and 0.7 nm.
 12. An apparatuscomprising: a substrate; a bottom electrode formed on the substrate; abase oxide layer formed on the bottom electrode; a first geometricconfining layer formed on the base oxide layer, wherein the firstgeometric confining layer comprises a first film comprising a firstplurality of pin-holes; and a top electrode formed on the firstgeometric confining layer and connected to a first top surface of thebase oxide layer via the first plurality of pin-holes, wherein the baseoxide layer comprises TaO_(x), HfO_(x), TiO_(x), ZrO_(x), or acombination thereof, wherein the first film of the first geometricconfining layer comprises Al₂O₃, SiO₂, Si₃N₄, Y₂O₃, Gd₂O₃, Sm₂O₃, CeO₂,Er₂O₃, or a combination thereof, and wherein a conductive filament formswithin the based oxide layer and in regions in alignment with the firstplurality of pin-holes when a set signal is applied to the top electrodeand the bottom electrode.
 13. The apparatus as claimed in claim 12,wherein the base oxide layer is at least three times as thick as thefirst geometric confining layer.
 14. The apparatus as claimed in claim12, wherein the first geometric confining layer does not grow uniformlyon a surface of the base oxide layer.